United thought they had pulled off one of the deals of the season last summer when they signed Falcao on a season-long loan from Monaco.

But eight months on, the club decided against signing the striker on a permanent basis after he scored just four goals in 29 appearances.

Falcao's wife Lorelei Taron posted a selfie on Instagram of her husband and their two young children in an airport departure lounge on Monday, the day after the club confirmed the 29-year-old would be leaving.

And the striker himself took to the picture-sharing website to give thanks to the fans who had backed him through his difficult year at Old Trafford.

"I wanna thank Manchester United and all its fans for every word and gesture of support they gave me in every match," the striker wrote underneath a picture of him celebrating in an United shirt.

The news that Falcao would be returning to Monaco following the season finale at Hull on Sunday hardly came as a surprise.

The forward, who missed the 0-0 draw at the KC Stadium through injury, was regarded as one of the most deadly marksmen in Europe after prolific spells at Porto, Atletico Madrid and Monaco, but he has struggled right from the start of his loan spell at United.

Former United striker Louis Saha admits keeping Falcao at Old Trafford after such a dour season would have made no sense.

"There was a question mark over him - the club would have been thinking 'Wait, hang on a minute, we are paying him a massive salary and if we pay him that amount again it's going to be a risk', so you can understand it in terms of business, it's normal."

Having suffered his fair share of knee injuries, Saha knows better than most just how hard it is to find form after a lengthy layoff.

He suspects Falcao has lost some of his spark due to anterior cruciate ligament damage he suffered in March last year.

"A cruciate injury is a disaster for a striker," said Saha, who scored 42 goals in 124 appearances for United.

"His turning and movement is a bit like Chicharito (Javier Hernandez) in the box, a bit explosive and you can't lose that.

"That's what happened at the end of my career. I was scoring less because I lost that little spark and once it's gone it's hard to find consistency.

"Basically that's why I stopped (playing) football."

Saha does not think Falcao's career is over, though. With a full pre-season campaign under his belt, the Frenchman thinks the two-time Ballon d'Or nominee could return to his best next term.

"His record before coming to United was a joke," said Saha, who also had spells with Everton, Tottenham, Newcastle, Sunderland and Fulham.

"I think he still remains a good goal scorer. It's vital for a striker to have a run of games.

"Look at (Luis) Suarez. He struggled for the first 10-15 games this year and he finished on fire.

"Barcelona gave him a platform. I don't think that he had that run of games at United but United is a club where they have to perform straight away, they are not here to wait for Falcao.

"He will score goals, for sure. Maybe the Premier League is the toughest to adapt to very sharply. After an injury it's not easy."